Process for coating and/or touching up coatings on metal surfaces

ABSTRACT

A composition and method for coating and touching up a metal surface is provided. The composition contains from about 0.5 to about 240 millimoles per kilograms of a fluorometallate ion, from about 0.5 grams/liters to about 10 grams/liter of phosphorous-containing inorganic oxy anions calculated at their stoichiometric equivalent as H3PO4; from about 0.05 g/l to about 3.5 g/l of hexavalent chromium and from about 0.10 g/l to about 2.20 g/l of trivalent chromium ions.

This application is a 371 of PCT/US98/17194 filed Aug. 21, 1998, whichclaims the benefit of U.S. Provisional Application No.60/056,488, filedAug. 21, 1997.

This invention relates to processes for treating a metal surface to forma protective coating, or for treating a metal surface on which aprotective coating has previously been formed and remains in place, withits protective qualities intact, on one part of the surface but istotally or partially absent from, or is present only in a damagedcondition over, one or more other parts of the surface, so that itsprotective value in these areas of at least partial damage or absencehas been diminished. (Usually the absence or damage of the initialprotective coating has been unintentional and has occurred as a resultof such events as imperfectly uniform formation of the initialprotective coating, mechanical damage of the initial protective coating,spotty exposure of the initially coated surface to solvents for theinitial protective coating, or the like. The absence or damage of theinitial protective coating may be intentional, however, as when holesare drilled in a coated surface, for example, or when untreated partsare attached to and therefore become part of a previously coatedsurface.) Particularly if the surface in question is large and thedamaged or untreated area(s) are relatively small, it is often moreeconomical to attempt to create or restore the full protective value ofthe original coating primarily in only the absent or damaged areas,without completely recoating the object. Such a process is generallyknown in the art, and will be briefly described herein, as “touching up”the surface in question. This invention is particularly well suited totouching up surfaces in which the original protective coating is aconversion coating initially formed on a primary metal surface, moreparticularly a primary metal surface consisting predominantly of iron,aluminum, and/or zinc.

An alternative or concurrent object of this invention is to provide aprocess for protectively coating metal surfaces that were neverpreviously coated. Other concurrent or alternative objects are toachieve at least as good protective qualities in the touched up areas asin those parts of the touched up surfaces where the initial protectivecoating is present and undamaged; to avoid any damage to anypre-existing protective coating from contacting it with the touching upcomposition; and to provide an economical touching up process. Otherobjects will be apparent to those skilled in the art from thedescription below.

Except in the claims and the operating examples, or where otherwiseexpressly indicated, all numerical quantities in this descriptionindicating amounts of material or conditions of reaction and/or use areto be understood as modified by the word “about” in describing thebroadest scope of the invention. Practice within the numerical limitsstated is generally preferred. Also, throughout this description, unlessexpressly stated to the contrary: percent, “parts of”, and ratio valuesare by weight; the term “polymer” includes “oligomer”, “copolymer”,“terpolymer”, and the like; the description of a group or class ofmaterials as suitable or preferred for a given purpose in connectionwith the invention implies that mixtures of any two or more of themembers of the group or class are equally suitable or preferred;description of constituents in chemical terms refers to the constituentsat the time of addition to any combination specified in the descriptionor of generation in situ by chemical reactions specified in thedescription, and does not necessarily preclude other chemicalinteractions among the constituents of a mixture once mixed;specification of materials in ionic form additionally implies thepresence of sufficient counterions to produce electrical neutrality forthe composition as a whole (any counterions thus implicitly specifiedshould preferably be selected from among other constituents explicitlyspecified in ionic form, to the extent possible; otherwise suchcounterions may be freely selected, except for avoiding counterions thatact adversely to the objects of the invention); and the term “mole” andits grammatical variations may be applied to elemental, ionic, and anyother chemical species defined by number and type of atoms present, aswell as to compounds with well defined molecules.

SUMMARY OF THE INVENTION

It has been found that excellent coating and/or touching up quality,particularly for corrosion resistance on previously untreated areas andcorrosion resistance in combination with a conversion coating, can beachieved by:

(I) covering the areas to be touched up with a layer of a liquidcomposition that comprises, preferably consists essentially of, or morepreferably consists of, water and:

(A) a component of fluorometallate anions, each of said anionsconsisting of:

(i) at least four fluorine atoms; and

(ii) at least one atom of an element selected from the group consistingof titanium, zirconium, hafnium, silicon, aluminum, and boron; and,optionally, one or both of

(iii) at least one ionizable hydrogen atom; and

(iv) at least one oxygen atom;

(B) a component of phosphorus-containing inorganic oxyanions and/orphosphonate anions; and

(C) a component of oxidizing agent or agents that are not part of eitherof immediately previously recited components (A) and (B) and are notchromium(III) cations;

and, optionally, one or more of the following components:

(D) chromium(III) cations;

(E) a component of free fluoride ions that are not part of any ofimmediately previously recited components (A) through (D);

(F) a component of surfactant molecules that are not part of any ofimmediately previously recited components (A) through (E);

(G) an acidifying component that is not part of any of the immediatelypreviously recited components (A) through (F); and

(H) a viscosity increasing component that is not part of any of theimmediately previously recited components (A) through (G);

and subsequently

(II) drying into place over the surface the liquid layer formed in step(I).

It should be understood that the components listed need not necessarilyall be provided by separate chemicals. For example, it is preferred thatthe fluorometallate anions and phosphorous-containing anions both beadded in the form of the corresponding acids, thereby also providing atleast some, and usually all, of optional acidifying component (G).

Various embodiments of the invention include processes for treatingsurfaces as described above, optionally in combination with otherprocess steps that may be conventional per se, such as precleaning,rinsing, and subsequent further protective coatings over those formedaccording to the invention, compositions useful for treating surfaces asdescribed above, and articles of manufacture including surfaces treatedaccording to a process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

For a variety of reasons, it is preferred that compositions usedaccording to the invention as defined above should be substantially freefrom many ingredients used in compositions for similar purposes in theprior art. Specifically, it is increasingly preferred in the ordergiven, independently for each preferably minimized component listedbelow, that these compositions, when directly contacted with metal in aprocess according to this invention, contain no more than 1.0, 0.35,0.10, 0.08, 0.06, 0.04, 0.02, 0.01, 0.005, 0.002, 0.001, 0.0005, or0.0002 percent of each of the following constituents: dispersed (in thisinstance not including truly dissolved) silica and/or silicates;ferricyanide; ferrocyanide; sulfates and sulfuric acid; anionscontaining molybdenum or tungsten; alkali metal and ammonium cations;pyrazole compounds; sugars; gluconic acid and its salts; glycerine;α-glucoheptanoic acid and its salts; and myoinositol phosphate estersand salts thereof.

A working composition for use in a process according to this inventionpreferably has a concentration of at least, with increasing preferencein the order given, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 4.8millimoles of fluorometallate anions, component (A), per kilogram oftotal working composition, this unit of concentration being freelyapplicable hereinafter to any other constituent as well as tofluorometallate anions and being hereinafter usually abbreviated as“mM/kg”; and if the maximum corrosion protection from a single treatmentwith a composition used in a process according to the invention isdesired as it often is, this concentration of fluorometallate anionsmore preferably is at least, with increasing preference in the ordergiven, 6.0, 7.0, 8.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0,18.0, 19.0, 20.0, 21.0, 22.0, 23.0, or 24. 0 mM/kg. Independently, in aworking composition, the concentration of fluorometallate ionspreferably, at least for economy, is not more than, with increasingpreference in the order given, 240, 150, 100, 80, 60, 50, 45, 40, 35,30, or 27 mM/kg, and if the working composition is intended for use in aprocess in which at least two treatments according to the invention willbe applied to the substrate, this concentration of fluorometallateanions still more preferably is not more than, with increasingpreference in the order given, 20, 15, 12, 10, 8.0, 7.0, 6.5, 6.0, 5.5,or 5.1 mM/kg.

Independently of their concentration, the fluorometallate anionspreferably are fluorosilicate (i.e., SiF₆ ⁻²), fluorotitanate (i.e.,TiF₆ ⁻²) or fluorozirconate (i.e., ZrF₆ ⁻²), more preferablyfluorotitanate or fluorozircoate, most preferably fluorozirconate.

Component (B) as defined above is to be understood as including all ofthe following inorganic acids and their salts and acid salts that may bepresent in the composition: hypophosphorous acid (H₃PO₂),orthophosphorous acid (H₃PO₃), pyrophosphoric acid (H₄P₂O₇),orthophosphoric acid (H₃PO₄), tripolyphosphoric acid (H₅P₃O₁₀), andfurther condensed phosphoric acids having the formulaH_(x+2)P_(x)O_(3x+1), where x is a positive integer greater than 3.Component (B) also includes all phosphonic acids and their salts.

Generally, inorganic phosphates, particularly orthophosphates,phosphites, hypophosphites, and/or pyrophosphates, especiallyorthophosphates, are preferred for component (B) because they are moreeconomical. Phosphonates are also suitable and may be advantageous foruse with very hard water, because the phosphonates are more effectivechelating agents for calcium ions. Acids and their salts in whichphosphorous has a valence less than five may be less stable than theothers to oxidizing agents and are therefore less preferred.

A composition according to the invention preferably contains at least,in increasing preference in the order given, 0.01, 0.05, 0.1, 0.2, 0.3,0.4, 0.5, 0.6, 0.65, or 0.70 parts, measured as its stoichiometricequivalent as H₃PO₄ of component (B) per thousand parts of totalcomposition, a concentration unit that may be freely used hereinafterfor other constituents and is hereinafter usually abbreviated as “ppt”.Independently, in a working composition used in a process according tothe invention, the concentration of component (B), measured as itsstoichiometric equivalent as H₃PO₄, preferably is not more than, inincreasing order of preference, 10, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0,2.0, 1.00, 0.90, or 0.80 ppt.

The oxidizing agent, component (C), preferably is selected from hydrogenperoxide; alkyl and other substituted peroxides; materials containinghexavalent chromium, such as chromates and dichromates; manganates andpermanganates; chlorates and perchlorates; iodates and periodates;nitrates; bromates and perbromates, molybdates, vanadates, and all ofthe acids corresponding to all of the previously listed anions in thissentence. Unless the use of hexavalent chromium as at least part ofoxidizing agent component (C) is barred because of fears of pollutionand/or personnel hazard, the use of hexavalent chromium is stronglypreferred. More particularly, the amount of hexavalent chromium presentin a working composition for use according to the invention, an amountwhich may readily be determined analytically by means known in the art,preferably is at least, with increasing preference in the order given,0.30, 0.50, 0.70, 1.00, 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, or 2.70grams of hexavalent chromium per liter of total working composition, aunit of measure which may be applied hereinafter to other components,and which is hereinafter usually abbreviated as “g/l.” Independently,the concentration of hexavalent chromium in a working composition usedin a process according to this invention preferably is not greater than,with increasing preference in the order given, 30, 25, 20, 15, 10, 8, 6,5.0, 4.0, 3.5, 3.3, 3.1, or 2.9 g/l.

Hexavalent chromium may be supplied to the working composition from anywater soluble source, including numerous available dichromate andchromate salts. However, at least for reasons of economy, the hexavalentchromium preferably is supplied as the chemical substance with theformula CrO₃, usually named “chromic acid” or “chromium trioxide”.

If the oxidizing agent component does not include hexavalent chromium,its “oxidizing power” should be adjusted to fall within the same rangeas is achieved in an alternative working composition by use of preferredamounts of hexavalent chromium as indicated above, together with allother necessary and preferred constituents as described herein. Theoxidizing power for this purpose may be conveniently measured by theelectrical potential of an inert metal electrode, such as a platinumelectrode, that is in physical contact with the liquid for which theoxidizing power is to be measured. The electrical potential of the inertmetal electrode is measured by comparison with a reference electrode ofknown conventionally established potential, by means known to thoseskilled in the art.

When oxidizing agent component (C) includes hexavalent chromium as itpreferably does, optional component (D) of chromium(III) cationspreferably is also used. At least one reason for this preference is thatthe presence of chromium(III) cations is useful in preventing, or atleast diminishing, leaching by water of the hexavalent chromium contentof the coating formed in a process according to this invention whenhexavalent chromium is a part of the treatment composition used. Thesource of the chromium(III) ions may be any soluble or solubilizablesource whose counterions do not interfere with the objects of theinvention. Soluble salts include the acetate, bromide hexahydrate,chloride hexahydrate, iodide, nitrate oxalate or sulfate ofchromium(III); complexes such as hexammine chromium(III) chloride, andothers which are chemically compatible with the coating composition.However, at least in part for economy, the chromium(III) cations presentin a composition used in a process according to this inventionpreferably are derived from in situ reduction of part of a source ofhexavalent chromium added to provide, from its unreduced portion, atleast part of component (C). Suitable reducing agents are well known tothose skilled in the art, with organic compounds, particularlyinexpensive carbohydrates such as sugar and starch, normally preferred.

The concentration of chromium(III) cations is preferably at least, inincreasing order of preference, 0.10, 0.25, 0.50, 0.75, 1.00, 1.25,1.50, 1.60, or 1.70 g/l. The ratio of hexavalent chromium atoms totrivalent chromium atoms in a composition to be used in a processaccording to this invention is preferably at least, in increasingpreference in the order given, 0.50:1.00, 0.75:1.00, 1.00:1.00,1.10:1.00, 1.20:1.00, 1.30:1.00, 1.40:1.00, 1.45:1.00, or 1.50:1.00 andindependently preferably is not more than, with increasing preference inthe order given, 20:1.00, 10:1.00, 5:1.00, 3.0:1.00, 2.5:1.00, or2.0:1.00. The total concentration of chromium atoms of any valence in aworking composition according to the invention is preferably at least,with increasing preference in the order given, 0.45, 0.60, 0.80, 1.2,1.5, 2.0, 2.5, 3.0, 3.5, 3.8, 4.0, or 4.4 g/l, and independently,primarily for reasons of economy, is preferably not more than, withincreasing preference in the order given, 50, 35, 20, 14, 10, 9.0, 8.0,7.0, 6.5, 6.0, 5.5, 5.0, or 4.6 g/l. Preferred amounts of chromium(III)cations in a working composition to be used according to the inventionmay be determined by subtracting from these numbers the values givenabove for the concentration of hexavalent chromium.

If the fluorometallate anions concentration exceeds 4.8 mM/kg in acomposition to be used in a process according to this invention,optional component (E) of free fluoride ions is preferably includedalso, unless the composition is to be used within a few days of havingbeen made. Otherwise, formation of a precipitate during storage of thecomposition is likely. This component may be supplied to the compositionby hydrofluoric acid or any of its partially or completely neutralizedsalts that are sufficiently water soluble. At least for economy,component (E) is preferably supplied by aqueous hydrofluoric acid, andindependently preferably is present in a concentration that is at least,with increasing preference in the order given, 0.10, 0.30, 0.50, 0.60,0.70, 0.80, or 0.90 ppt of its stoichiometric equivalent as HF.Independently, in a working composition to be used in a processaccording to the invention, the concentration of component (E), measuredas its stoichiometric equivalent as HF, preferably is not more than,with increasing preference in the order given, 10, 8.0, 6.0, 4.0, 3.0,2.0, 1.5, 1.3, or 1.1 ppt.

Component (F), if used, is chosen from anionic surfactants, such assalts of carboxylic acids, alkylsulphonates, alkyl-substitutedphenylsulphonates; nonionic surfactants, such as alkyl-substituteddiphenylacetylenic alcohols and nonylphenol polyoxyethylenes; andcationic surfactants such as alkylammonium salts; all of these may andpreferably do contain fluorine atoms bonded directly to carbon atoms intheir molecules. Each molecule of a surfactant used preferably containsa hydrophobe portion that (i) is bonded by a continuous chain and/orring of covalent bonds; (ii) contains a number of carbon atoms that isat least, with increasing preference in the order given, 10, 12, 14, or16 and independently preferably is not more than, with increasingpreference in the order given, 30, 26, 22, or 20; and (iii) contains noother atoms except hydrogen, halogen, and ether-bonded oxygen atoms.Component (F) is most preferably a fluorinated alkyl ester such asFLUORAD™ FC 430, a material commercially supplied by Minnesota Miningand Manufacturing Co.

A working composition according to the invention preferably contains,with increasing preference in the order given, at least 0.010, 0.030,0.050, 0.070, 0.080, 0.090, or 0.100 ppt of component (F) andindependently preferably, primarily for reasons of economy, contains notmore than, with increasing preference in the order given, 5.0, 2.5,1.30, 0.80, 0.60, 0.40, 0.30, 0.20, 0.18, 0.15, 0.13, or 0.11 ppt ofcomponent (F).

The pH of a composition used according to the invention preferably is atleast, with increasing preference in the order given, 0.10, 0.30, 0.50,0.70, 0.90, 1.10, 1.20, 1.30, 1.40, 1.50, 1.55, or 1.60 andindependently preferably is not more than, with increasing preference inthe order given, 5.0, 4.0, 3.5, 3.0, 2.90, 2.80, 2.70, 2.60, 2.50, 2.40,2.30, 2.20, 2.10, 2.00, 1.90, 1.80, or 1.70. Ordinarily, a preferred pHwill result automatically from use of preferred concentrations ofhexavalent chromium, phosphate ions, fluorometallate anions, and freefluoride ions supplied to the composition from preferred acidic sourcesas already noted. If, however, in some particular instance a preferredpH value is not achieved in this manner, other acidifying agents arewell known in the art and may be used as optional component (G). Thiscomponent, however, is normally preferably omitted, at least foreconomy.

Dilute compositions, within these preferred ranges, that include thenecessary active ingredients (A) through (C) only may have inadequateviscosity to be self-supporting in the desired thickness for touching upareas that can not be placed in a substantially horizontal positionduring treatment and drying; if so, one of the materials known in theart, such as natural gums, synthetic polymers, colloidal solids, or thelike should be used as optional component (H), as is generally known inthe art, unless sufficient viscosity is provided by one or more of otheroptional components of the composition. If the characteristic treatmentcomposition is to be applied in a process according to the invention byuse of a saturated felt or like material, component (H) is rarely neededand usually is preferably omitted, because most viscosity increasingagents are susceptible to being at least partially filtered out of thetreatment composition by applicators of this type.

A working composition according to the invention may be applied to ametal workpiece and dried thereon by any convenient method, several ofwhich will be readily apparent to those skilled in the art. For example,coating the metal with a liquid film may be accomplished by immersingthe surface in a container of the liquid composition, spraying thecomposition on the surface, coating the surface by passing it betweenupper and lower rollers with the lower roller immersed in a container ofthe liquid composition, contact with a brush or felt saturated with theliquid treatment composition, and the like, or by a mixture of methods.Excessive amounts of the liquid composition that might otherwise remainon the surface prior to drying may be removed before drying by anyconvenient method, such as drainage under the influence of gravity,passing between rolls, and the like.

A particularly advantageous method of application of the treatmentliquid in a process according to this invention makes use of anapplicator as disclosed in U.S. Pat. No. 5,702,759 of Dec. 30, 1997 toWhite et al., the entire disclosure of which, except for any part thatmay be inconsistent with any explicit statement herein, is herebyincorporated herein by reference.

The temperature during application of the liquid composition may be anytemperature within the liquid range of the composition, although forconvenience and economy in application, normal room temperature, i.e.,from 20-27° C., is usually preferred.

Preferably the amount of composition applied in a process according tothis invention is chosen so as to result, after drying into place, in atleast as good corrosion resistance for the parts of the surface treatedaccording to the invention as in the parts of the same surface where theinitial protective coating is present and a process according to theinvention has not been applied. Ordinarily, for most common protectivephosphate and chromate conversion coatings as initial protectivecoatings, such protection will be achieved if the total add-on mass(after drying) of the coating applied in a process according to theinvention is at least, with increasing preference in the order given,0.005, 0.010, 0.015, 0.020, 0.025, 0.030, 0.035, 0.040, 0.045, 0.050,0.055, or 0.060 grams per square meter of surface coated (hereinafterusually abbreviated as “g/m²”). Independently, at least equal corrosionresistance ordinarily will be achieved even if the add-on mass is not,and therefore for reasons of economy the add-on mass preferably is notgreater than, with increasing preference in the order given, 1.00, 0.70,0.50, 0.30, 0.20, 0.15, 0.10, 0.090, 0.085, 0.080, or 0.075 g/m².

The add-on mass of the protective film formed by a process according tothe invention may be conveniently monitored and controlled by measuringthe add-on weight or mass of the metal atoms in the anions of component(A) as defined above, or of chromium when that is part of component (C)of the treatment composition used, except in the unusual instances whenthe initial protective coating and/or the underlying metal substratecontains the same metal element(s). The amount of these metal atoms maybe measured by any of several conventional analytical techniques knownto those skilled in the art. The most reliable measurements generallyinvolve dissolving the coating from a known area of coated substrate anddetermining the content of the metal of interest in the resultingsolution. The total add-on mass can then be calculated from the knownrelationship between the amount of the metal in component (A) and thetotal mass of the part of the total composition that remains afterdrying. However, this method is often impractical for use with thisinvention, because the area touched up is not always precisely defined.A more practical alternative is generally provided by small area X-rayspectrographs that, after conventional calibration, directly measure theamount(s) per unit area of individual metallic element(s) present in acoating, free from almost all interferences except the same elementspresent in other coatings on, or in a thin layer near the surface of,the underlying metal surface itself.

In many instances sufficiently precise control of the amount of coatingused can be determined visually from the color of the area coated,because most preferred compositions for use according to the inventionare fairly strongly colored. Unless the surface to be treated happens tobe the same or a similar color, the amount of active ingredients cantherefore be estimated by the intensity of the color of the liquid filmformed in a process according to the invention.

The effectiveness of a treatment according to the invention appears todepend predominantly on the total amounts of the active ingredients thatare dried in place on each unit area of the treated surface, and on thenature of the active ingredients and their ratios to one another, ratherthan on the concentration of the acidic aqueous composition used, andthe speed of drying has not been observed to have any technical effecton the invention, although it may well be important for economicreasons. If practical in view of the size of the object treated and thesize of the areas of the object to be treated, drying may be speeded byplacement of the surface to be treated, either before or afterapplication to the surface of a liquid composition in a processaccording to the invention, in an oven, use of radiative or microwaveheating, or the like. If speed of treatment is desired, but placing theentire object in an oven is inconvenient, a portable source of hot airor radiation may be used in the touched up area(s) only. In eitherinstance, heating the surface before treatment is preferred over heatingafter treatment when practical, and prewarming temperatures up to atleast 65° C. may be satisfactorily used. If ample time is available atacceptable economic cost, a liquid film applied according to thisinvention often may simply be allowed to dry spontaneously in theambient atmosphere with equally good results insofar as the protectivequality of the coating is concerned. Suitable methods for eachcircumstance will be readily apparent to those skilled in the art.

Preferably, the surface to be treated according to the invention isfirst cleaned of any contaminants, particularly organic contaminants andforeign metal fines and/or inclusions. Such cleaning may be accomplishedby methods known to those skilled in the art and adapted to theparticular type of substrate to be treated. For example, for galvanizedsteel surfaces, the substrate is most preferably cleaned with aconventional hot alkaline cleaner, then rinsed with hot water and dried.For aluminum, the surface to be treated most preferably is firstcontacted with a conventional hot alkaline cleaner, then rinsed in hotwater, then, optionally, contacted with a neutralizing acid rinse and/ordeoxidized, before being contacted with an acid aqueous composition asdescribed above. Ordinarily, cleaning methods suitable for theunderlying metals will also be satisfactory for any part of the initialprotective coating that is also coated in a process according to theinvention, but care should be taken to choose a cleaning method andcomposition that do not themselves damage the protective qualities ofthe initial protective coating in areas that are not to be touched up.If the initial protective coating is thick enough, the surface can besatisfactorily cleaned by physically abrading, as with sandpaper oranother coated abrasive, the area(s) to be touched up and any desiredoverlap zone where the initial protective coating is still in placearound the damaged areas to be touched up. The swarf may then be removedby blowing, brushing, rinsing, or with attachment to a cleaning tool,such as a moist cloth. It has been found that, when dry abrasion is usedas the last preparatory cleaning method, the corrosion resistance of thecoating usually will be less than optimal and the coating will appearsmutty. However, dry abrasion followed by rinsing is a satisfactory andoften preferred cleaning method. One indication that the surface issufficiently clean is that a film of water sprayed on the surface willdry without beading.

After the preparatory cleaning, the surface may be dried by absorptionof the cleaning fluid, evaporation, or any suitable method known tothose skilled in the art. Corrosion resistance is usually less thanoptimal when there is a delay between the preparatory cleaning, orcleaning and drying, and the coating of the surface. The time betweencleaning, or cleaning and drying, and coating the surface should be nomore than, in increasing order of preference, 48, 24, 6.0, 5.0, 4.0,3.0, 2.0, 1.0, 0.50, 0.25, or 0.1 hours.

Usually, it is preferable, as a precaution during a touch up processaccording to the invention, to apply the composition used for touchingup not only to obviously bare metal or obviously damaged areas of theinitial protective coating, but also over a transition or overlap zoneof apparently undamaged initial protective coating adjacent to suchareas that obviously need touching up. With increasing preference in theorder given, such a transition zone has a width that is at least 0.2,0.5, 0.7, 1.0, 1.5, or 2.0 millimeters and independently preferably,primarily for reasons of economy, is not more than, with increasingpreference in the order given, 25, 20, 15, 10, 8.0, 6.0, 5.0, or 3.0millimeters.

Virtually any kind of initial protective coating can be touched upeffectively for many purposes by a process according to this invention.In particular, but without limitation, conversion coatings produced onunderlying metal according to the teachings of any one of the followingU.S. Patents, the disclosures of all of which, except to any extent thatthey may be inconsistent with any explicit statement herein, are herebyincorporated herein by reference, may be effectively touched up by aprocess according to this invention: U.S. Pat. No. 5,769,667 of Jun. 23,1998 to Dolan; U.S. Pat. No. 5,700,334 of Dec. 23, 1997 to Ishii et at;U.S. Pat. No. 5,645,650 of Jul. 8, 1997 to Ishizaki et al.; U.S. Pat.No. 5,683,816 of Nov. 4, 1997 to Goodreau; U.S. Pat. No. 5,595,611 ofJan. 21, 1997 to Boulos et al.; U.S. Pat. No. 5,551,994 of Sep. 3, 1996to Schriever; U.S. Pat. No. 5,534,082 of Jul. 9, 1996 to Dollman et al.;U.S. Pat. No. 5,507,084 of Apr. 16, 1996 to Ogino et al.; U.S. Pat. No.5,498,759 of Mar. 12,1996 to Nakada et al.; U.S. Pat. No. 5,498,300 ofMar. 12, 1996 to Aoki et al.; U.S. Pat. No. 5,487,949 of Jan. 30, 1996to Schriever, U.S. Pat. No. 5,472,524 of Dec. 5, 1995; U.S. Pat. No.5,472,522 of Dec. 5, 1995 to Kawaguchi et at; U.S. Pat. No. 5,452,884 ofOct. 3, 1995; U.S. Pat. No. 5,451,271 of Sep. 19, 1995 to Yoshida etal.; U.S. Pat. No. 5,449,415 of Sep. 19, 1995 to Dolan; U.S. Pat. No.5,449,414 of Sep. 12, 1995 to Dolan; U.S. Pat. No. 5,427,632 of Jun. 27,1995 to Dolan; U.S. Pat. No. 5,415,687 of May 16, 1995 to Schriever;U.S. Pat. No. 5,411,606 of May 2, 1995 to Schriever; U.S. Pat. No.5,399,209 of Mar. 21, 1995 to Suda et al.; U.S. Pat. No. 5,395,655 ofMar. 7, 1995 to Kazuyuki et al.; U.S. Pat. No. 5,391,239 of Feb. 21,1995 to Boulos; U.S. Pat. No. 5,378,392 of Jan. 3, 1995 to Miller etal.; U.S. Pat. No. 5,366,567 of Nov. 22, 1994 to Ogino et al.; U.S. Pat.No. 5,356,490 of Oct. 18, 1994 to Dolan et al.; U.S. Pat. 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A process according to this invention is particularly advantageouslyapplied to touching up a surface in which the undamaged parts areprotected by a coating selected from the group consisting of a phosphateconversion coating, a chromate conversion coating, and a conversioncoating produced by contacting a predominantly aluminiferous or apredominantly zinciferous surface with an acidic treating solutioncomprising at least one of fluorosilicate, fluorotitanate, andfluorozirconate.

In addition, of course, metal surfaces with any other type of previouslyapplied protective coating or without any previous deliberately appliedcoating can be coated in a process according to the invention.

The practice of this invention may be further appreciated byconsideration of the following, non-limiting, working examples.

GROUP 1

In this group, a preferred type of base solution for making up workingcompositions for use in a process according to the invention was firstprepared as follows: 0.94 part of pearl cornstarch was slurried togetherwith 8.00 parts of deionized (hereinafter usually abbreviated as “DI”)water. In a separate container, 300 parts of DI water, 8.56 parts ofchromic acid (i.e., CrO₃) crystals, and 1.00 part of an aqueous solutioncontaining 75% of H₃PO₄ were mixed together. The previously preparedslurried starch mixture was then added to the other mixture, and all ofthe thus formed new mixture was heated to boiling temperature, withstirring and reflux condensation of evaporating water, and boiled for 90minutes to assure complete reaction of the starch. Later analysis showedthat 5.2 parts out of the originally added 8.56 parts of chromic acidremained in hexavalent form after this reaction (and any reaction thatmay have occurred with other ingredients added later to make a completeworking composition for use according to this invention). The remainderof the initially added chromium is presumed to have been reduced tochromium(III) cations that remain dissolved in the solution. (The onlysignificant product derived from the starch under these reactionconditions is believed to be carbon dioxide that escapes into theatmosphere, but if any non-volatile product is formed and remains in theproduct after boiling, any such residue from the starch does not harmthe use of the product or essentially change the nature of theinvention.)

TABLE 1 Ingredient Concentration in Ppt of Ingredient in WorkingComposition H₂ZrF₆ 5.0 1.00 H₂SiF₆ 5.0 1.00 FeF₃ 0.093 HF 1.00 0.50 0.10H₂O₂ 0.15 H₂MoO₄ 5.0 1.00

The base solution prepared as described in the immediately precedingparagraph was used to form candidate working position according to theinvention by adding one of the materials noted in Table 1 to a portionof this base solution, which is diluted, using DI water, along withthese additions so that the “parts” of ingredients, other than starchand the fraction of the initially added chromic acid modified byreaction with starch, that were used to make the base solution, asspecified above, are present in 1000 total parts of the final workingcomposition. (All of the chromium atoms contained in the chromic acidoriginally used are believed to remain in the solution, with those atomsnot having been reduced to a trivalent form remaining as hexavalentchromium atoms, which may be present as unchanged chromic acid and/or aschromate and/or condensed chromate anions. All of the forms ofhexavalent chromium present in these solutions are believed to besubstantially equally effective in forming a protective coating in aprocess according to this invention.)

Surfaces of conventional rectangular (7.6×25 centimeters) sheet testpieces of Types 7075, 6061, and/or 2024-T3 aluminum were treatedaccording to the invention, after preparatory cleaning and othertreatment as follows.

Each panel was placed on a non-slip surface of plastic webbing overabsorbent towels, and a rectangular (5.1×7.6 centimeters) Scotch-Brite™96 Very Fine green lofty non-woven coated abrasive pad, saturated withwater, was used to uniformly scrub the panel lengthwise, using longstraight strokes of slight to moderate pressure. The pad was then rinsedwell with clean tap water (and left water-saturated) and, using the sameside and end of the pad, the panel was rubbed with similar strokes inthe crosswise direction. The pad was rinsed again and, using the sameside of the pad but the fresh end, the panel was scrubbed in thelengthwise direction once again with similar strokes. The panel was thenrinsed briefly with water and subsequently wiped dry with a freshabsorbent paper wiper. The panel was set aside and the pad rinsed well.(The opposite side of the pad was used in the same way on the nextpanel, and the pad was then discarded.)

After two panels had been cleaned and dried, a first treatment accordingto the invention was applied over the cleaned panel surface in thelengthwise direction, from an applicator as described in U.S. Pat. No.5,702,759, using even strokes with a 50% overlap. Moderate and evenpressure (not nearly enough to activate the valve in the applicator) wasused, because using such moderate and even pressure facilitates formingan even coating that has little tendency to dewet. While this coat wasdrying, another two panels were usually cleaned as described in theimmediately preceding paragraph. Usually by the time two more panels hadbeen cleaned, the once coated panels were ready for their second coat.The second coat was applied in the crosswise direction, and then the twofreshly cleaned panels were given their first coat.

The treated panels were subjected to salt spray testing and werevisually rated qualitatively only for corrosion resistance. Thecorrosion resistance decreased from the top to the bottom of Table 1according to this rating, but all of the panels would be satisfactoryfor many uses.

GROUP 2

In this group, the more promising additives from Group 1 wereinvestigated more thoroughly, along with an organic polymer resin andsome combinations of these materials. The base solution was the same asfor Group 1, except for the addition of FLUO-RAD™ 430 in an amountcorresponding to 0.1 ppt of the final working composition, and theadditional constituent or constituents are shown in Table 2. In thistable, the abbreviation “AC-73” means RHOPLEX™ AC-73, an acrylic polymeremulsion commercially supplied by Rohm & Haas and reported by itssupplier to contain 46-47% of ultimate resin solids.

TABLE 2 Identifying Number Content of H₂ZrF₆ Content of HF Content ofAC-73 1 1.0 ppt 0 0 2 5.0 ppt 0 0 3 1.0 ppt 1.0 ppt 0 4 1.0 ppt 0 20 ppt5 5.0 ppt 0 20 ppt 6 5.0 ppt 1.0 ppt 20 ppt 7 3.0 ppt 0 0 8 3.0 ppt 1.0ppt 0 9 0 0 10 10 7.5 ppt 1.0 ppt 0 11  10 ppt 1.0 ppt 0 12 5.0 ppt 0.10ppt 0 13 5.0 ppt 0.25. ppt 0 14 5.0 ppt 0.50 ppt 0 15 5.0 ppt 0.75 ppt 0

Test substrates were conventional flat panels of Type 2024 aluminumalloy supplied by Advanced Coating Technologies (“ACT”) and AluminumCompany of America (“ALCOA”) or of Type 7075 aluminum alloy supplied byALCOA or Kaiser Aluminum Company (“Kaiser”). These were prepared andtreated in the same manner as in Group 1, except that a second treatmentaccording to the invention was applied on only half of each substratepanel, so that the effects of both single and double treatments could beevaluated on each panel. The coated panels were then subjected for 504hours to salt spray testing according to American Society for Testingand Material Procedure B 117, except that the tested panels weremaintained at an angle 6° from vertical during their exposure asprescribed by MIL-C-5541E. Results are shown in Table 3.

TABLE 3 Identifi- Rating after 504 Hours of Salt Spray for Substrate:cation ACT 2024 with: ALCOA 2024 with: ALCOA 7075 with: Kaiser 7075with: Number 1 Coat 2 Coats 1 Coat 2 Coats 1 Coat 2 Coats 1 Coat 2 Coats1 10% D, SP 1% D 5% D Good 10% D  1% D 5% D 1% D, P 2  5% D, SP Good 5%D Good 5% D Good 5% D Good 3 1% D Good Good Good 2% D Good 2% D Good 41% D Good 2% D Good 5% D Good 2% D Good 5 3% D Good 2% D Good 5% D,PGood Good Good 6 5% D Good 2% D Good SP Good Good Good 7 20% D  GoodGood Good SP Good Good Good 8 2% D Good 1% D Good SP Good Good Good 910% D  Good 5% D Good 1% D Good 5% D Good 10 2% D Good 1% D Good 0.5% DGood 2% D Good 11 Good Good Good Good SP Good 2% D Good 12 1% D Good 3%D Good SP Good Good Good 13 Good Good 1% D Good 5% D, P Good 1% D Good14 Good Good 1% D Good 2% D, P Good 1% D Good 15 1% D 1% D 1% D GoodGood 1 small pit 1% D Good Abbreviations and Other Notes for Table 3 “D”means “discoloration”; “SP” means “small pits”; “P” means “pits”; “Good”indicates no pits or discoloration, except sometimes within 0.5centimeters of the exposed edge, an area which is to be ignoredaccording to the test specifications.

The results in Table 3 suggest that more than 1 ppt of fluorozirconicacid is usually required to achieve excellent corrosion resistance in asingle coating, but that even with higher concentrations offluorozirconic acid, these higher quality results are not consistentlyachieved. (There are at least two apparent possible causes for thisinconsistency: slight variations in substrate composition andunavoidable inconsistencies in the manual application of coating used.Other unrecognized causes are also possible, of course.) On the otherhand, most of the compositions give excellent results with two coats.This suggests that for touching-up processes, where at least two coatsare likely to be used in any event to insure a uniform and fullyprotective coating, a concentration near 1.0 ppt is likely to be mostpreferred, because it is more economical than a higher concentration andgives good results if used at least twice. For coating previouslyunprotected metal, in contrast, if the coating conditions can bearranged with reliable control, as in conventional continuous processingof coils, for example, and a consistently suitable substrate is used,higher concentrations of fluorozirconic acid would normally bepreferred, because compositions with such higher concentrations can giveexcellent corrosion protection in a single coating operation.

GROUP 3

In this group, the storage stability of some candidate treatmentcompositions to be used according to the invention was explored. Thecompositions were made with the same base solution as for Group 2, withthe concentrations of hydrofluoric acid and fluorozirconic acid shown inTable 4. Each composition was placed in a closed container at 49° C. andmaintained at that temperature by storage in a thermostaticallycontrolled oven. Each container was examined daily for at least 30 days,unless the formation of a solid precipitate was observed sooner. Whenprecipitate was observed, the storage stability test was ended. Resultsare shown in Table 4.

TABLE 4 Concentration in Parts per Thousand of: Days Stored before AnyHF H₂ZrF₆ Visible Precipitate Formed 0.10 5.0 3 0.25 5.0 13 0.50 5.0 >300.75 5.0 >30 1.0 3.0 >30 1.0 5.0 >30 1.0 75 >30 1.0 10 >30

The results in Table 4 indicate that at least 0.50 ppt of HF is requiredto stabilize a composition that contains at least 5.0 ppt of H₂ZrF₆against formation of a precipitate during storage under practical useconditions.

The invention claimed is:
 1. A composition for coating or touching up orboth coating and touching up a metal surface, said compositioncomprising water and: (A) from about 0.5 millimoles per kilogram toabout 240 millimoles per kilogram, a unit hereafter abbreviated as“mM/kg” of a component of fluorometallate anions, each of said anionsconsisting of: (i) at least four fluorine atoms; and (ii) at least oneatom of an element selected from the group consisting of titanium,zirconium, hafnium, silicon, aluminum, and boron, and, optionally, oneor both of (iii) at least one ionizable hydrogen atom; and (iv) at leastone oxygen atom; (B) from about 0.5 grams/liter to about 10 grams/liter,a unit hereafter abbreviated as g/l, of a component ofphosphorus-containing inorganic oxyanions or phosphonate anions or bothphosphorus-containing inorganic oxyanions and phosphonate anionscalculated as the stoichiometric equivalent of H₃PO₄; and (C) from about0.5 g/l to about 3.5 g/l of hexavalent chromium, (D) from about 0.10 g/lto about 2.20 g/l of trivalent chromium cations; said liquid compositioncomprising not more than 0.06% of dispersed silica and silicates.
 2. Thecomposition according to claim 1, wherein: the fluorometallate anionsare selected from the group consisting of fluorosilicate,fluorotitanate, and fluorozirconate anions.
 3. The composition accordingto claim 1, wherein: the fluorometallate anions include fluorozirconateanions; the concentration of fluorozirconate anions is within a rangefrom about 3.5 to about 6.0 mM/kg, inclusive of 3.5 and 6.0 mM/kg; thetotal concentration of phosphorus-containing inorganic oxyanions andphosphonate anions, calculated as their stoichiometric equivalent asH₃PO₄ is within a range from about 0.50 to about 1.00 g/l, inclusive of0.50 and 1.00 g/l; the concentration of hexavalent chromium is within arange from about 2.25 to about 3.5 g/l, inclusive of 2.25 and 3.5 g/l;the concentration of chromium(III) cations is within a range from about1.25 to about 2.20 g/l, inclusive of 1.25 and 2.20 g/l; wherein a ratioof hexavalent chromium to chromium(III) ions is within a range fromabout 2.5:1.00 to about 1.30:1.00, inclusive of 2.5:1.00 and 1.30:1.00.4. The composition according to claim 3 which further includesfluorinated alkyl ester surfactant molecules in a concentration that iswithin a range from about 0.070 to about 0.13 parts per thousand, atunit hereinafter abbreviated as “ppt”, said range being inclusive of0.070 and 0.13 ppt.
 5. The composition according to claim 1, wherein:the fluorometallate anions include fluorozirconate anions; theconcentration of fluorozirconate anions is within a range from about18.0 to about 30.0 mM/kg, inclusive of 18.0 and 30.0 mM/kg; the totalconcentration of phosphorus-containing inorganic oxyanions andphosphonate anions, calculated as their stoichiometric equivalent asH₃PO₄ is within a range from about 0.50 to about 1.00 g/l, inclusive of0.50 and 1.00 g/l; the concentration of hexavalent chromium is within arange from about 2.25 to about 3.5 g/l, inclusive of 2.25 and 3.5 g/l;the concentration of chromium(III) cations is within a range from about1.25 to about 2.20 g/l, inclusive of 1.25 and 2.20 g/l; wherein a ratioof hexavalent chromium to chromium(III) ions is within a range fromabout 2.5:1.00 to about 1.30:1.00, inclusive of 2.5:1.00 and 1.30:1.00;and further including from about 0.70 ppt to about 1.3 ppt ofhydrofluoric acid, inclusive of 0.70 and 1.3 ppt.
 6. The compositionaccording to claim 5 which further includes from about 0.070 ppt toabout 0.13 ppt fluorinated alkyl ester surfactant molecules inclusive of0.070 and 0.13 ppt.
 7. A composition for coating or touching up or bothcoating and touching up a metal surface, said composition being made bymixing together a first mass of water and at least the followingcomponents: (A) a second mass of a water-soluble source offluorometallate anions to provide in the composition from about 0.5mM/kg to about 240 mM/kg of the fluorometallate anion, each of saidanions consisting of: (i) at least four fluorine atoms; and (ii) atleast one atom of an element selected from the group consisting oftitanium, zirconium, hafnium, silicon, aluminum, and boron; and,optionally, one or both of (iii) at least one ionizable hydrogen atom,and (iv) at least one oxygen atom; (B) a third mass of one or morewater-soluble sources of phosphorus-containing inorganic oxyanions,phosphonate anions or both phosphorus-containing inorganic oxyanions andphosphonate anions; to provide in the composition from about 0.5 g/l toabout 10 g/l, calculated as their stoichiontic equivalent of H₃PO₄; and(C) a fourth mass of a water-soluble source of hexavalent chromiumcations to provide the composition with from about 0.5 g/l to about 3.5g/l of hexavalent chromium cation, (D) a fifth mass of a component toprovide the composition with from about 0.10 g/l to about 2.20 g/l ofchromium(III) cation.
 8. The composition according to claim 7, wherein:the fourth mass comprises hexavalent chromium in an amount thatcorresponds, after any reaction with any reducing agents for hexavalentchromium that are mixed together with it to constitute said composition,to a concentration of residual hexavalent chromium in said compositionthat is within a range from about 0.50 g/l to about 3.5 g/l.
 9. Thecomposition according to claim 8, wherein: the second mass comprisesfluorozirconate anions in an amount that corresponds to a concentration,in said composition, that is within a range from about 3.50 mM/kg toabout 6.0 mM/kg, inclusive of 3.50 mM/kg and 6.0 mM/kg; the third masscorresponds to a total concentration of phosphorus-containing inorganicoxyanions and phosphonate anions, calculated as their stoichiometricequivalent as H₃PO₄, that is within a range from about 0.50 to about1.00 g/l, inclusive of 0.50 and 1.00 g/l; the fourth mass compriseschromic acid in an amount that: corresponds to a total concentration, insaid composition, of hexavalent chromium ions that is within a rangefrom about 2.25 to about 3.5 g/l, inclusive of 2.25 and 3.5 g/l; is thesource of hexavalent chromium for the composition; and together with asixth mass of reducing agent that is also mixed into the composition, isalso the source of the trivalent chromium ions for the composition, andsaid sixth mass of reducing agent corresponds stoichiometrically, in itsreaction with chromic acid, to a concentration, in said composition, ofchromium(III) ions that is within a range from about 1.25 mM/kg to about2.20 mM/kg, inclusive of 1.25 mM/kg and 2.20 mM/kg; wherein a ratio ofhexavalent chromium to chromium(III) ions that is within a range fromabout 2.5:1.00 to about 1.30:1.00, inclusive of 2.5:1.00 and 1.30:1.00;there is also mixed into said composition a seventh mass of fluorinatedalkyl ester surfactant molecules that corresponds to a concentration, insaid composition, that is within a range from about 0.070 to about 0.13ppt, inclusive of 0.070 and 0.13 ppt.
 10. The composition according toclaim 7, wherein: the second mass comprises fluorozirconate anions in anamount that corresponds to a concentration, in said composition, offluorozirconate anions that is within a range from about 18 mM/kg toabout 30 mM/kg, inclusive of 18 and 30 mM/kg; the third mass correspondsto a total concentration of phosphorus-containing inorganic oxyanionsand phosphonate anions, calculated as its stoichiometric equivalent asH₃PO₄, that is within a range from about 0.50 to about 1.00 g/l,inclusive of 0.50 and 1.00 g/l; the fourth mass comprises chromic acidin an amount that: corresponds to a total concentration, in saidcomposition, of hexavalent chromium atoms that is within a range fromabout 2.25 to about 3.5 g/l, inclusive of 2.25 and 3.5 g/l; is thesource of hexavalent chromium for the composition; and together with asixth mass of reducing agent that is also mixed into the composition, isalso the source of the trivalent chromium ions for the composition; andsaid sixth mass of reducing agent corresponds stoichiometrically, in itsreaction with chromic acid, to a concentration, in said composition, ofchromium(III) ions that is within a range from about 1.25 to about 2.20g/l, inclusive of 1.25 and 2.20 g/l; there is a ratio of hexavalentchromium to chromium(III) ions that is within a range from about2.5:1.00 to about 1.30:1.00, inclusive of 2.5:1.00 and 1.30:1.00; thereis additionally mixed into said composition an eighth mass ofhydrofluoric acid that corresponds to a concentration, in saidcomposition, that is within a range from about 0.70 to about 1.3 ppt,inclusive of 0.70 and 1.3 ppt; and there is also mixed into saidcomposition a seventh mass of fluorinated alkyl ester surfactantmolecules that corresponds to a concentration, in said composition, thatis within a range from about 0.070 to about 0.13 ppt, inclusive of 0.070and 0.13 ppt.
 11. A process for coating or touching up or both coatingand touching up a surface, said surface comprising at least one area ofbare metal, at least one area of coating over an underlying metalsubstrate, or both of at least one area of bare metal and at least onearea of coating over an underlying metal substrate, said processcomprising operations of: (I) covering the surface to be coated, touchedup, or both coated and touched up with a layer of a liquid compositionof claim 1; and (II) drying the liquid layer formed in operation (I).12. The process according to claim 11, wherein: the surface comprises atleast one area of bare metal and at least one area of coating over anunderlying metal substrate; and in operation (I), the liquid layer isformed over the at least one area of bare metal.
 13. The processaccording to claim 11, wherein, in said liquid composition used inoperation (I): the fluorometallate anions are selected from the groupconsisting of fluorosilicate, fluorotitanate, and fluorozirconateanions.
 14. The process according to claim 11, wherein, in said liquidcomposition used in operation (I): the fluorometallate anions includefluorozirconate anions; the concentration of fluorozirconate anions iswithin a range from about 3.5 to about 6.0 mM/kg, inclusive of 3.5 and6.0 mM/kg, the total concentration of phosphorus-containing inorganicoxyanions and phosphonate anions, calculated as their stoichiometricequivalent as H₃PO₄, is within a range from about 0.50 to about 1.00g/l, inclusive of 0.50 and 1.00 g/l; the concentration of hexavalentchromium is within a range from about 2.25 to about 3.5 g/l, inclusiveof 2.25 and 3.5 g/l; the concentration of chromium(III) ions is within arange from about 1.25 to about 2.20 g/l, inclusive of 1.25 and 2.20 g/l;and wherein, a ratio of hexavalent chromium to chromium(III) ions iswithin a range from about 2.5:1.00 to about 1.30:1.00, inclusive of2.5:1.00 and 1.30:1.00; and the composition further includes asurfactant comprising fluorinated alkyl ester molecules in aconcentration that is within a range from about 0.070 to about 0.13 ppt,inclusive of 0.070 and 0.13 ppt.
 15. The process according to claim 14,wherein: the surface comprises at least one area of bare metal adjacentto at least one area of coating over an underlying metal substrate, saidat least one area of coating over an underlying metal substratecomprising a first portion and a second portion, in operation (I), theliquid layer is formed over both the area of bare metal and at least thefirst portion of said adjacent area of coating over an underlying metalsubstrate; and the coating over an underlying metal substrate isselected from the group consisting of a phosphate conversion coating, achromate conversion coating, and a conversion coating produced bycontacting a predominantly aluminiferous or a predominantly zinciferoussurface with an acidic treating solution comprising at least one offluorosilicate, fluorotitanate, and fluorozirconate.
 16. The processaccording to claim 13, wherein, in the liquid composition used inoperation (I): the fluorometallate anions include fluorozirconateanions; the concentration of fluorozirconate anions is within a rangefrom about 18.0 to about 30 mM/kg inclusive of 18.0 and 30.0 mM/kg; thetotal concentration of phosphorus-containing inorganic oxyanions andphosphonate anions, calculated as their stoichiometric equivalent asH₃PO₄, is within a range from about 0.50 to about 1.00 g/l, inclusive of0.50 and 1.00 g/l; the concentration of hexavalent chromium is within arange from about 2.25 to about 3.5 g/l, inclusive of 2.25 and 3.5 g/l;the concentration of chromium(III) ions is within a range from about1.25 to about 2.20 g/l, inclusive of 1.25 and 2.20 g/l; a ratio ofhexavalent chromium to chromium(III) ions that is within a range fromabout 2.5:1.00 to about 1.30:1.00, inclusive of 2.5:1.00 and 1.30:1.00;a concentration of hydrofluoric acid that is within a range from about0.70 to about 1.3 ppt, inclusive of 0.70 and 1.3 ppt; and wherein thecomposition includes fluorinated alkyl ester surfactant molecules in aconcentration that is within a range from about 0.070 to about 0.13 ppt,inclusive of 0.070 and 0.13 ppt.
 17. A process for coating or touchingup or both coating and touching up a surface, said surface comprising atleast one area of bare metal, at least one area of coating over anunderlying metal substrate, or both of at least one area of bare metaland at least one area of coating over an underlying metal substrate,said process comprising operations of: (I) covering the areas to becoated, touched up, or both coated and touched up with a layer of aliquid composition, said liquid composition having been made by mixingtogether a first mass of water and at least the following components:(A) a second mass of a water-soluble source of fluorometallate anions toprovide in the composition from about 0.5 mM/kg to about 30 mM/kg of thefluorometallate anion, each of said anions consisting of: (i) at leastfour fluorine atoms; and (ii) at least one atom of an element selectedfrom the group consisting of titanium, zirconium, hafnium, silicon,aluminum, and boron; and, optionally, one or both of (iii) at least oneionizable hydrogen atom; and (iv) at least one oxygen atom; (B) a thirdmass of one or more water-soluble sources of phosphorus-containinginorganic oxyanions, phosphonate anions or both phosphorus-containinginorganic oxyanions and phosphonate anions; to provide in thecomposition from about 0.5 g/l to about 10 g/l, calculated as theirstoichiontic equivalent or H₃PO₄; and (C) a fourth mass of awater-soluble source of hexavalent chromium cations to provide thecomposition with from about 0.5 g/l to about 3.5 g/l of hexavalentchromium cation; (D) a fifth mass of component to provide thecomposition with from about 0.10 g/l to about 2.20 g/l of chromium(III)cation, said composition not comprising more than about 0.060% ofdispersed silica and silicates; and (II) drying into place over thesurface the liquid layer formed in operation (I).
 18. The processaccording to claim 17, wherein: the surface comprises at least one areaof bare metal and at least one area of coating over an underlying metalsubstrate; and in operation (I), the liquid layer is formed over the atleast one area of bare metal.
 19. The process according to claim 17,wherein the liquid composition further comprises from about 0.70 toabout 1.3 ppt of hydrofluoric acid.
 20. The process according to claim19, wherein: the second mass comprises fluorozirconate anions in anamount that corresponds to a concentration, in said composition, that iswithin a range from about 3.50 mM/kg to about 6.0 mM/kg, inclusive of3.50 and 6.0 mM/kg; the third mass corresponds to a total concentrationof phosphorus-containing inorganic oxyanions and phosphonate anions,calculated as their stoichiometric equivalent as H₃PO₄, that is within arange from about 0.50 to about 1.00 g/l, inclusive of 0.50 and 1.00 g/l;the fourth mass comprises chromic acid in an amount that: corresponds toa total concentration, in said composition, of hexavalent chromiumcations that is within a range from about 2.25 to about 3.5 g/l,inclusive of 2.25 and 3.5 g/l; is the source of hexavalent chromium forthe composition; and together with a sixth mass of reducing agent thatis also mixed into the composition, is also the source of the trivalentchromium ions for the composition; and said sixth mass of reducing agentcorresponds stoichiometrically, in its reaction with chromic acid, to aconcentration, in said composition, of chromium(III) ions that is withina range from about 1.25 to about 2.20 g/l, inclusive of 1.25 and 2.20g/l; wherein a ratio of hexavalent chromium to chromium(III) ions iswithin a range from about 2.5:1.00 to about 1.30:1.00, inclusive of2.5:1.00 and 1.30:1.00; there is also mixed into said composition aseventh mass of fluorinated alkyl ester surfactant molecules thatcorresponds to a concentration, in said composition, that is within arange from about 0.070 to about 0.13 ppt, inclusive of 0.070 and 0.13ppt.
 21. The process according to claim 20, wherein: the surfacecomprises at least one area of bare metal adjacent to at least one areaof coating over an underlying metal substrate, said at least one area ofcoating over an underlying metal substrate comprising a first portionand a second portion; in operation (I), the liquid layer is formed overboth the area of bare metal and at least the first portion of saidadjacent area of coating over an underlying metal substrate; and thecoating over an underlying metal substrate is selected from the groupconsisting of a phosphate conversion coating, a chromate conversioncoating, and a conversion coating produced by contacting a predominantlyaluminiferous or a predominantly zinciferous surface with an acidictreating solution comprising at least one of fluorosilicate,fluorotitanate, and fluorozirconate.
 22. The process according to claim19, wherein: the second mass comprises fluorozirconate anions in anamount that corresponds to a concentration, in said composition, offluorozirconate anions that is within a range from about 18 to about 30mM/kg, inclusive of 18 and 30 mM/kg; the third mass corresponds to atotal condition of phosphorus-containing inorganic oxyanions andphosphonate anions, calculated as its stoichiometric equivalent asH₃PO₄, that is within a range from about 0.50 to about 1.00 g/l,inclusive of 0.50 and 1.00 g/l; the fourth mass comprises chromic acidin an amount that: corresponds to a total concentration, in saidcomposition, of hexavalent chromium cations within a range from about2.25 to about 3.5 g/l, inclusive of 2.25 and 3.5 g/l; is the source ofhexavalent chromium for the composition; and together with a sixth massof reducing agent that is also mixed into the composition, is also thesource of the trivalent chromium ions for the composition; and saidsixth mass of reducing agent corresponds stoichiometrically, in itsreaction with chromic acid, to a concentration, in said composition, ofchromium(III) ions that is within a range from about 1.25 to about 2.20g/l, inclusive of 1.25 and 2.20 g/l; in said liquid composition, thereis a ratio of hexavalent chromium to chromium(III) ions that is within arange from about 2.5:1.00 to about 1.30:1.00, inclusive of 2.5:1.00 and1.30:1.00; there is additionally mixed into said composition an eighthmass of hydrofluoric acid that corresponds to a concentration, in saidcomposition, that is within a range from about 0.70 to about 1.3 ppt,inclusive of 0.70 and 1.3 ppt; there is also mixed into said compositiona seventh mass of fluorinated alkyl ester surfactant molecules thatcorresponds to a concentration, in said composition, that is within arange from about 0.070 to about 0.13 ppt, inclusive of 0.070 and 0.13ppt.